A coordinated action involving eleven stations of the ground -based Network for Detection of Stratospheric Change (NDSC) equipped with Fourier transform infrared (FTIR) instruments was conducted to contribute to the validation of the three atmospheric chemistry instruments onboard ENVISAT, that are MIPAS, SCIAMACHY and GOMOS. The target products for validation are total columns of O3, CH4, CO and some important NOy species (NO2, HNO3, NO) and the source gas N2O. Together the eleven stations cover the latitudes between 79 °N and 78°S, including polar, mid-latitude and subtropical and tropical locations. The goal is to contribute to the assessment of the data quality of the aforementioned ENVISAT instruments, from a quasi -global perspective. The period of intensive ground-based data collection for the benefit of the ENVISAT Validation Commissioning Phase that is dealt with in the present paper is July 15 to December 1, 2002. The FTIR network involved collected a data set corresponding to an equivalent of approximately 400 days of measurements; about three quarter of the data have already been submitted to the ENVISAT Calval database and are included in the present work. Unfortunately, the distribution of ENVISAT data has been slow and limited. Only a limited number of coincidences has been found for making data inter -comparisons. Therefore, the conclusions drawn in this paper are very preliminary and cover only a limited set of data products from SCIAMACHY only. Our findings up to now concerning the above mentioned target products are the following: (1) SCIAMACHY near infrared operational products (CO, CH4, N 2O) have no scientific meaning yet, (2), the operational SCIAMACHY total vertical O3 column product derived in the ultraviolet window has undergone some improvements with changing versions of the processor(s) but it still underestimates the column by about 5 – 10 %, (3), the operational SCIAMACHY total vertical O3 column product derived in the visible window is unrealistically large, and (4), the operational NO2 total column product from SCIAMACHY seems to largely overestimate the real column, but very few coincidences and large dispersions of the data do inhibit any further conclusion at present. In a next phase, the same ground-based correlative data set will be exploited to further validate the ENVISAT data as soon as more and reprocessed data will be distributed. [less ▲]

Since the middle of the 20th century, the University of Liège has been active at the International Scientific Station of the Jungfraujoch (ISSJ) in the Swiss Alps (46.5°N, 8.0°E, 3580m asl) to study the ... [more ▼]

Since the middle of the 20th century, the University of Liège has been active at the International Scientific Station of the Jungfraujoch (ISSJ) in the Swiss Alps (46.5°N, 8.0°E, 3580m asl) to study the chemical composition of both the solar photosphere and the Earth’s atmosphere. Since 1989, the ISSJ is an accepted site of the northern midlattitude primary Alpine station of the NDSC (Network for the Detection of Stratospheric Change). This acceptance resulted from earlier monitoring activities by Ulg of a large number of atmospheric constituents. Within the NDSC frame, a special attention and many efforts have been devoted to the monitoring of the most important atmospheric constituents involved both in the erosion of stratospheric ozone and in the greenhouse capacity of the troposphere, after it became clear that human activities have a direct impact on these two processes. Using two high resolution Fourier transform infrared (FTIR) spectrometers, over 25000 wide-band solar spectra encompassing nearly 1700 days since the mid 1980s have been recorded and analyzed to study, quasi simultaneously and repeatedly, local, seasonal and secular variations of some 20 gaseous telluric species. So far, most results have been reported, demonstrating the power of infrared spectrometric solar observations to characterize the chemical composition of the atmosphere. These datas, archived in terms of total vertical column abundances (e.g., at the NDSC-Data Host Facility; http://www.ndsc.ws), are expressed in number molecules per cm2 above the site using best-know input parameters (i.e. spectroscopic-, instrumental-, environmental-) in the retrieval procedure. Meanwhile, more sophisticated algorithms, based on the “Rodgers” optimal estimation method, have been developed, allowing to derive partial tropospheric- and stratospheric columns for various species, including HCl, ClONO2, O3, HF, CO, N2O, CH4, HCN, OCS. This contribution reports related results for HCl and ClONO2. [less ▲]

A coordinated action involving eleven stations of the ground-based Network for Detection of Stratospheric Change (NDSC) equipped with Fourier transform infrared (FTIR) instruments was conducted to contribute to the validation of the three atmospheric chemistry instruments onboard ENVISAT, that are MIPAS, SCIAMACHY and GOMOS. The target products for validation are total columns of O3, CH4, CO and some important NOy species (NO2, HNO3, NO) and the source gas N2O. Together the eleven stations cover the latitudes between 79 °N and 78°S, including polar, mid -latitude and subtropical and tropical locations. The goal is to contribute to the assessment of the data quality of the aforementioned ENVISAT instruments, from a quasi-global perspective. The period of intensive ground-based data collection for the benefit of the ENVISAT Validation Commissioning Phase that is dealt with in the present paper is July 15 to December 1, 2002. The FTIR network involved collected a data set corresponding to an equivalent of approximately 400 days of measurements; about three quarter of the data have already been submitted to the ENVISAT Calval database and are included in the present work. Unfortunately, the distribution of ENVISAT data has been slow and limited. Only a limited number of coincidences has been found for making data inter-comparisons. Therefore, the conclusions drawn in this paper are very preliminary and cover only a limited set of data products from SCIAMACHY only. Our findings up to now concerning the above mentioned target products are the following: (1) SCIAMACHY near infrared operational products (CO, CH4, N2O) have no scientific meaning yet, (2), the operational SCIAMACHY total vertical O3 column product derived in the ultraviolet window has undergone some improvements with changing versions of the processor(s) but it still underestimates the column by about 5 – 10 %, (3), the operational SCIAMACHY total vertical O3 column product derived in the visible window is unrealistically large, and (3), the operational NO2 total column product from SCIAMACHY seems to largely overestimate the real column, but very few coincidences and large dispersions of the data do inhibit any further conclusion at present. In a next phase, the same ground-based correlative data set will be exploited to further validate the ENVISAT data as soon as more and reprocessed data will be distributed. [less ▲]

Version 3 of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment data set for some 30 trace and minor gas profiles is available. From the IR solar-absorption spectra measured during four Space ... [more ▼]

Version 3 of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment data set for some 30 trace and minor gas profiles is available. From the IR solar-absorption spectra measured during four Space Shuttle missions (in 1985, 1992, 1993, and 1994), profiles from more than 350 occultations were retrieved from the upper troposphere to the lower mesosphere. Previous results were unreliable for tropospheric retrievals, but with a new global-fitting algorithm profiles are reliably returned down to altitudes as low as 6.5 km (clouds permitting) and include notably improved retrievals of H2O, CO, and other species. Results for stratospheric water are more consistent across the ATMOS spectral filters and do not indicate a net consumption of H-2 in the upper stratosphere. A new sulfuric-acid aerosol product is described. An overview of ATMOS Version 3 processing is presented with a discussion of estimated uncertainties. Differences between these Version 3 and previously reported Version 2 ATMOS results are discussed. Retrievals are available at http://atmos.jpl.nasa.gov/atmos. (C) 2002 Optical Society of America. [less ▲]

[1] Solar absorption spectra recorded over a 24-year time span have been analyzed to retrieve average free tropospheric mixing ratios of carbonyl sulfide (OCS). The measurements were recorded with the ... [more ▼]

[1] Solar absorption spectra recorded over a 24-year time span have been analyzed to retrieve average free tropospheric mixing ratios of carbonyl sulfide (OCS). The measurements were recorded with the Fourier transform spectrometer located in the U. S. National Solar Observatory McMath solar telescope facility on Kitt Peak (altitude 2.09 km, lat. 31.9degreesN, long. 111.6degreesW), southwest of Tucson, Arizona, and were obtained on 167 days between May 1978 and February 2002, typically at 0.01-cm(-1) spectral resolution. A best fit to the time series shows an average mixing ratio of 566 pptv (1 pptv = 10(-12) per unit volume) between 2.09 and 10 km, a small but statistically significant long-term decrease equal to (-0.25 +/- 0.04)% yr(-1), 1 sigma, and a seasonal variation with a summer maximum, a winter minimum, and a peak amplitude of (1.3 +/- 0.4)%, 1 sigma, relative to the mean. Although a statistically significant decline and seasonal variation have been detected, both are exceedingly small. The present results confirm and extend earlier studies showing that the OCS free tropospheric abundance at northern midlatitudes has remained nearly constant over the last decades. [less ▲]

Time series of stratospheric hydrogen fluoride (HF) column abundances have been derived from infrared solar absorption spectra recorded for 195 days between May 1977 and June 2001 at a spectral resolution ... [more ▼]

Time series of stratospheric hydrogen fluoride (HF) column abundances have been derived from infrared solar absorption spectra recorded for 195 days between May 1977 and June 2001 at a spectral resolution of typically 0.01 cm(-1). The measurements were made at the US National Solar Observatory facility on Kitt Peak, Arizona, USA (31.9degreesN, 111.6degreesW, 2.09 km altitude) and have been analyzed with the SFIT2 algorithm, which is based on a semi-empirical application of the optimal estimation method. The measurements show a continuous buildup of the stratospheric HF column over the 24-yr period superimposed on short-term variations and a seasonal cycle with spring maxima and autumn minima. The measured stratospheric HF columns increased by a factor of 4.7, from 2.03 x 10(14) molecule cm(-2) in May 1977 to 9.49 x 10(14) molecule cm(-2) in June 2001. A best fit with a model that assumes an exponential increase in the stratospheric HF column with time superimposed on a sinusoidal seasonal cycle yields an average rate of stratospheric HF column increase of (4.30 +/- 0.15% yr(-1)), 1 sigma. The rate of increase is nearly a factor of two less than that derived previously from 1977 to 1990 Kitt Peak total columns, which indicates a significant slowdown in the increase rate during the 1990s, consistent with the trends from recent near-global lower mesospheric satellite remote and surface in situ measurements. Day-to-day stratospheric HIT columns are highly correlated with the same day stratospheric HCl columns as a result of common transport of lower and higher latitude air to above the station. Extrapolation of the linear relation between the two sets of stratospheric columns indicates a background HCl column of 1 x 10(15) molecule cm(-2) for zero HF, consistent with a previous estimate from 1977 to 1990 HF and HCl Kitt Peak total column measurements and a 1973 HCl measurement above the station. (C) 2002 Elsevier Science Ltd. All rights reserved. [less ▲]

[1] Near-simultaneous, 0.0035 or 0.007 cm(-1) resolution infrared solar absorption spectra of tropospheric HCN, C2H2, CO, and C2H6 have been recorded from the Network for the Detection of Stratospheric ... [more ▼]

[1] Near-simultaneous, 0.0035 or 0.007 cm(-1) resolution infrared solar absorption spectra of tropospheric HCN, C2H2, CO, and C2H6 have been recorded from the Network for the Detection of Stratospheric Change station in Lauder, New Zealand (45.04degreesS, 169.68degreesE, 0.37 km altitude). All four molecules were measured on over 350 days with HCN and C2H2 reported for the first time based on a new analysis procedure that significantly increases the effective signal-to-noise of weak tropospheric absorption features in the measured spectra. The CO measurements extend by 2.5 years a database of measurements begun in January 1994 for CO with improved sensitivity in the lower and middle troposphere. The C2H6 measurements lengthen a time series begun in July 1993 with peak sensitivity in the upper troposphere. Retrievals of all four molecules were obtained with an algorithm based on the semiempirical application of the Rodgers optimal estimation technique. Columns are reported for the 0.37- to 12-km-altitude region, approximately the troposphere above the station. The seasonal cycles of all four molecules are asymmetric, with minima in March-June and sharp peaks and increased variability during August-November, which corresponds to the period of maximum biomass burning near the end of the Southern Hemisphere tropical dry season. Except for a possible HCN column decrease, no evidence was found for a statistically significant long-term trend. [less ▲]

[1] We have compared a new version of Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) retrievals (version 3) of stratospheric and mesospheric water vapor with observations from shuttleborne ... [more ▼]

[1] We have compared a new version of Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) retrievals (version 3) of stratospheric and mesospheric water vapor with observations from shuttleborne, satelliteborne, balloonborne, and aircraftborne instruments. These retrievals show agreement to within 5% with the MkIV observations in the middle and lower stratosphere. ATMOS agrees with the National Oceanic and Atmospheric Administration (NOAA) Lyman-alpha hygrometer to within 5% except for features with spatial scales less than the vertical resolution of ATMOS (such as the lower stratospheric seasonal cycle). ATMOS observations are 10-16% lower than measurements from the Harvard Lyman-alpha hygrometer in the lower stratosphere and are 7-14% higher than those from the Microwave Limb Sounder (MLS; prototype version 0104) throughout most of the stratosphere. Agreement is within 7% with the Millimeter-Wave Atmospheric Sounder (MAS; version 20) in the middle and upper stratosphere, but differences are closer to 13% in the lower stratosphere. Throughout the stratosphere, agreement is within 8% with the Halogen Occultation Experiment (HALOE; version 19). ATMOS data from 1994 show agreement with the Stratospheric Aerosol and Gas Experiment II (SAGE II; version 6) values to within 8% in the middle stratosphere, but ATMOS observations are systematically higher than those from SAGE II by as much as 41% in the lower stratosphere. In contrast, ATMOS 1985 values are systematically similar to50% lower than SAGE II values from sunset occultations in the lower stratosphere near 70 hPa but appear to be in better agreement with sunrise occultations. Version 3 retrievals in the upper stratosphere and lower mesosphere are typically 5-10% lower than version 2 values between 1 and 0.05 hPa. This reduction improves agreement with HALOE, MAS, and MLS upper atmospheric observations, but ATMOS values still tend to be higher than values from these instruments in the middle mesosphere. Agreement among the instruments compared here (except for SAGE II) is generally within 15% in the middle to lower stratosphere and mesosphere and within 10% in the middle to upper stratosphere. At altitudes near 30 km, all instruments (including SAGE II) agree to within 10%. [less ▲]

This paper gives a brief description and “raison d’être” of the Network for the Detection of Stratospheric Change (NDSC) as well as its key research tasks to address the broader goal of monitoring ... [more ▼]

This paper gives a brief description and “raison d’être” of the Network for the Detection of Stratospheric Change (NDSC) as well as its key research tasks to address the broader goal of monitoring atmospheric changes and to identify their causes and related impacts on mankind’s environment. While the Network has primarily focussed, thus far, on monitoring the ozone layer and assessing global compliance with the Montreal Protocol, ongoing implementations and new capabilities have enabled it to adapt to more recent political developments such as the Kyoto Proto-col on substances affecting the climate system. Examples of activities in support of the latter are reported, based on infrared solar observations at the Jungfraujoch station. [less ▲]

The main objective of this work was to determine the inorganic chlorine budget (Cly) at northern midlatitudes, to establish its variability and to study its temporal evolution over the last fifteen years ... [more ▼]

The main objective of this work was to determine the inorganic chlorine budget (Cly) at northern midlatitudes, to establish its variability and to study its temporal evolution over the last fifteen years. To achieve this, we have analyzed the observational database made of IR solar spectra recorded mainly with high resolution Fourier transform spectrometers installed at the International Scientific Station of the Jungfraujoch, located in the Swiss Alps, at 3580m altitude. The analysis of ATMOS (Atmospheric Trace Molecule Spectroscopy) data allowed us to first establish that HCl and ClONO2 account for more than 93% of the total inorganic chlorine, and that the summation of their vertical column abundances is an excellent surrogate of the Cly evolution at midlatitudes. Thus, we have derived HCl and ClONO2 total column abundance time series above the Jungfraujoch to analyze their temporal evolutions. Their combination has allowed us to show that the Cly increase between 1986 and 1995 (+50%) resulted primarily from the photodissociation of long-lived chlorinated source gas, in particular the manmade chlorofluorocarbons (CFC), progressively transported to the stratosphere after their release at the Earth surface during the seventies and the eighties. The organic chlorine (CCly) decrease in the troposphere resulting from regulations adopted by the Montreal Protocol, its Amendments and Adjustments, led to a progressive stabilization of Cly in the stratosphere. However, statistical analysis and interannual variability characterizing our time series, which extend to the end of 2000, prevent any final determination of the occurrence of the Cly maximum observed here at the end of October 1996, and of its subsequent decrease. We also show that chlorine partitioning among the chlorinated reservoirs has been durably influenced by heterogeneous processes which took place on stratospheric aerosols significantly enhanced following strong volcanic eruption of Mt Pinatubo (Philippines) in June 1991. The above-mentioned topics, complementary findings resulting from the study of the evolution of inorganic fluorine in the stratosphere, as well as comparisons other observational data bases and 2D model predictions are essentially discussed in Chapter 4. Before, Chapter 1 briefly reviews physical and chemical properties of the Earth atmosphere, and processes that control the state and erosion of stratospheric ozone. Individual contributions of chlorinated source gases to the CCly budget and their temporal evolution to the latter, inventory of Cly species, phase out schedule of chemical compounds covered by the Montreal Protocol and its Amendments and Adjustments are given in Chapter 2. Chapter 3 deals with instrumentation and data processing descriptions used to produce the geophysical data sets exploited in the main chapter of this work. [less ▲]

in Abstracts presented at the NDSC 2001 Symposium: Celebrating 10 years of atmospheric research (2001)

Based on high-resolution solar spectra recorded with FTIR instruments at the University of Liège laboratory located at the Jungfraujoch NDSC station (Swiss Alps, 46.5ºN, 8ºE, altitude 3580 m), the most ... [more ▼]

Based on high-resolution solar spectra recorded with FTIR instruments at the University of Liège laboratory located at the Jungfraujoch NDSC station (Swiss Alps, 46.5ºN, 8ºE, altitude 3580 m), the most important constituents making up the NOy family have been measured consistently since the mid-1980s. They include HNO3, NO, NO2 and ClONO2, which are analyzed in terms of their vertical column abundances above the site. Related trends have been determined and assessed statistically. Among these, only ClONO2 and NO2 reveal significant long-term trends. The combined column evaluation of NOy indicates a rate of change equal to (0.1+/-0.2) %/year, thus statistically undefined and barely consistent with the evolution of the source gas N2O. Trends derived from the observations will be compared critically with those deduced from a long-term run of a 2-D stratospheric model developed at the University of Oslo. The model includes full gaseous chemistry, PSCs and sulfate particles, which vary from year to year. Comparisons with similar data found in the literature are also discussed. [less ▲]

Free tropospheric HCN columns have been derived from infrared solar spectra recorded with the National Solar Observatory Fourier transform spectrometer on Kitt Peak, Arizona (31.9ºN latitude, 111.6ºW longitude, 2.09 km altitude) between May 1978 and May 2000. The time series show up to a factor of 2.4 enhancement during the strong El Ninos of 1982-1983 and 1997-1998, the most intense since 1970. The observations provide confirmation that HCN is a sensitive tracer of biomass burning emissions transported to the free troposphere. No statistically significant long-term trend in the HCN-free tropospheric column has been detected over the 22-year measurement period. The results illustrate the importance of long-term spectroscopic measurements for quantifying climate and atmospheric chemistry-related atmospheric changes. [less ▲]

Time series of free tropospheric carbon monoxide (CO), ethane (C2H6), and hydrogen cyanide (HCN) column abundances have been derived from observations at the International Scientific Station of the ... [more ▼]

Time series of free tropospheric carbon monoxide (CO), ethane (C2H6), and hydrogen cyanide (HCN) column abundances have been derived from observations at the International Scientific Station of the Jungfraujoch (ISSJ) at 3.58-km altitude in the Swiss Alps (latitude 46.55 degreesN, 7.98 degreesE longitude). The free troposphere was assumed to extend from 3.58 to 11 km altitude, and the related columns were derived for all three molecules from high spectral resolution infrared solar spectra recorded between January 1995 and October 1999. The three molecules show distinct seasonal cycles with maxima during winter for CO and C2H6, and during spring for HCN. These seasonal changes are superimposed on interannual variations. The tropospheric columns of all three molecules were elevated during 1998. Increases were most pronounced for HCN with enhanced values throughout the year, up to a factor of 2 in January 1998 when compared to averages of the other years. The increased tropospheric columns coincide with the period of widespread wildfires during the strong El Nino warm phase of 1997-1998. The emission enhancements above ISSJ are less pronounced, and they peaked after the increases measured above Mauna Loa (19.55 degreesN, 155.6 degreesW). Tropospheric trends for CO, C2H6, and HCN of (2.40 +/- 0.49), (0.47 +/- 0.64), and (7.00 +/- 1.61)% yr(-1)(1 sigma) were derived for January 1995 to October 1999. However, if 1998 measurements are excluded from the fit, CO and HCN trends that are not statistically significant, and a statistically significant decrease in the C2H6 tropospheric column, are inferred. Comparisons of the infrared CO columns with CO in situ surface measurements suggest that the CO free tropospheric vertical Volume mixing ratio profile generally decreases with altitude throughout the year. [less ▲]

Comparisons of chemically active species with chemically inert tracers are useful to quantify transport and mixing and assess the accuracy of model predictions. We report measurements of chemically active ... [more ▼]

Comparisons of chemically active species with chemically inert tracers are useful to quantify transport and mixing and assess the accuracy of model predictions. We report measurements of chemically active species and chemically inert tracers in the stratosphere derived from the analysis of infrared solar absorption spectra recorded with a ground-based Fourier transform spectrometer operated typically at 0.005- to 0.01-cm(-1) spectral resolution. The measurements were recorded from Kitt Peak in southern Arizona (latitude 31.9 degrees N, 111.6 degrees W, 2.09 km altitude). Time series of N2O, CH4, O3, and HNO3 vertical profiles have been retrieved from measurements in microwindows. From these results, correlations between N2O and CH4 stratospheric mixing ratios and between O3 and HNO3 lower stratospheric mixing ratios have been derived. The measured correlations between N2O versus CH4 mixing ratios are compact and show little variability with respect to season in quantitative agreement with Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) spring and autumn measurements recorded near the same latitude. Lower stratospheric O3 versus HNO3 mixing ratios measured during low to moderate aerosol loading time periods also show a compact relations though the HNO3/O3 slope is a factor of 2 lower than obtained from November 1994 ATMOS measurements near the Same latitude. We also compare Kitt Peak and ATMOS N2O versus CH4 and O3 versus HNO3 relations obtained by averaging the measurements over two broad stratospheric layers. This comparison avoids bias from the a priori profiles and the limited vertical resolution of the ground-based observations. [less ▲]

We characterize the spring and fall stratospheric distribution of CO at 49 degrees N-55 degrees S latitude from ATMOS profiles measured during 4 shuttle flights, Measured mixing ratios increase with potential temperature (theta) from 12 ppbv (10(-9) per unit volume) at 525 K, to 30-40 ppbv at 1750 K with only minor variations with latitude and season at a theta level. Evidence for some confinement near 1150 K in the developing November 1994 vortex is indicated from comparison of CO and N2O horizontal gradients. Measured CO mixing ratios at the tropical tropopause are a factor of 10 higher than values calculated with a steady-state model using standard photochemistry constrained by correlative temperatures and pressures, and ATMOS measurements including CH4 as inputs, Differences decrease with latitude at constant theta and are <20% at 800 K and all latitudes, where the CO photochemical lifetime is 40-50 days. [less ▲]

The study of series of ground-based solar observations performed within the frame of the NDSC indicates that the rate of increase of the atmospheric loading of inorganic chlorine has progressively slowed ... [more ▼]

The study of series of ground-based solar observations performed within the frame of the NDSC indicates that the rate of increase of the atmospheric loading of inorganic chlorine has progressively slowed down, then stabilized around 1996-97, with a subsequent tendency towards a decrease. The investigation is based on total column abundances of HCl and ClONO2 measured at the Jungfraujoch station in the Swiss Alps and on stratospheric columns of HCl derived from observations at Kitt Peak National Observatory (Arizona, USA). The observed changes are compared with near-global observations of HCl around the stratopause by HALOE and with a global, best-case emission scenario of Cl-bearing ground-level source gases compiled by UNEP [less ▲]